1. Field of the Invention
This invention relates to the field of illumination systems and more specifically to a sealed lighting system wherein the entire lighting system including lighting tubes, ballast and wiring is completely sealed from the surrounding environment.
2. Prior Art
Sealed lighting systems are widely used in harsh or hazardous environments where the lighting systems are exposed to high levels of moisture, corrosive or explosive compounds. For example, sealed lighting systems are often used in marine environments wherein the high humidity and salt content of the ambient environment easily corrodes electrical components. Similarly, in many industrial environments, airborne explosive compounds may be easily ignited by electrical sparks. Accordingly, sealed lighting fixtures are employed to prevent interaction between electrical components and the surrounding environment. Finally, sealed lighting fixtures are often used in hostile environments wherein lighting elements may be prone to fractures due to mechanical impacts.
One type of sealed lighting fixture is disclosed in U.S. Pat. No. 4,435,744--Russo. This reference discloses a fluorescent light fixture sealed from an environment in which explosive vapors are present to prevent sparks from the fixture from detonating the vapors. The apparatus comprises a plurality of globes into which fluorescent tubes are inserted, wherein the respective globes are bolted into a fixture at either end. The apparatus incorporates spring biased endcaps to facilitate the removal of inoperative fluorescent tubes. Wiring for providing power to the fluorescent lamps is routed to the fluorescent lamps through channels formed in the end attachment pieces. This system has several problems. In order to replace a lamp, the entire unit including the globe and end pieces must be unbolted from the fixture. While unbolting the endcaps, undesirable stress may be placed on the associated wiring, thus affecting the reliability of the system. Furthermore, the apparatus of Russo is constructed of either aluminum alloy, brass or brass alloy. Accordingly, this apparatus is prone to corrosion in many environments.
Another type of sealed lighting system is described in U.S. Pat. No. 4,851,972--Altman. This system incorporates a transparent tube of plastic polymeric material. Within the tube are a series of miniature lamps. The ends of the tube, which contain the electrical connectors, are sealed with a hardened thermoplastic potting compound. Moisture-free gas is injected into the tube through a hole in the tube wall. The existing air in the tube is forced out through another hole in the tube wall. The holes are then sealed to trap the moisture-free gas within the tube and prevent moisture from entering therein. While this system provides a moisture resistant lighting structure, it has several deficiencies. Since miniature lamps are used in the structure, limited light is produced by the structure. Furthermore, since the structure is sealed with thermoplastic material, the entire structure must be discarded when the lamps burn out.
Still another type of sealed lighting fixture is described in U.S. Pat. No. 4,547,839--Ripley et al. This reference discloses an outdoor lighting fixture for a circular fluorescent lamp. This device comprises a circular base containing a socket into which the lamp is inserted. The base contains a lip wherein a hollow transparent casing of cylindrical shape is placed over the base to protect the lamp, the casing being seated around the lip on the base. The lamp thus resides within a closed protected casing which is sealed from environmental factors. While this apparatus provides environmental protection for a circular fluorescent lamp, no means are disclosed for protecting associated electrical circuitry for powering the lamp.
From the foregoing, no method or apparatus is known which provides environmental protection for both a lamp and associated electrical circuitry, in a sealed assembly which is constructed with non-corrosive materials, and which is easily opened for servicing without the need for disassembling the structure or disturbing the internal wiring of the apparatus.